body { background:#222; color:#fff; text-align:center; }
#game-area { width:600px; height:400px; margin:20px auto; background:#333; position:relative; overflow:hidden; }
#player { width:30px; height:30px; background:lime; position:absolute; bottom:20px; left:285px; }
.enemy { width:30px; height:30px; background:red; position:absolute; top:0; }